A typical fiber optic cable includes a fiber for carrying light from one end to the other. In general, the fiber includes a core, a surrounding cladding and an outer jacket. Typically, the core is translucent material (e.g., glass, plastic, etc.) through which pulses of light (i.e., representing binary data) can propagate. The surrounding cladding includes material similar to that of the core but provides a lower refractive index than that of the core in order to cause properly angled light within the core to reflect back into the core with minimal light energy loss. The outer jacket (or buffer) protects and strengthens the cable.
A fiber optic connector typically resides at each end of the fiber optic cable. Such a connector typically includes a precision molded component called a ferrule (e.g., an MT ferrule). The ferrule, which is typically made out of metal, ceramic, plastic, or a combination of ceramic and plastic, holds the end of the fiber (i.e., the end of the fiber core and cladding) using epoxy or solder. The connector precisely positions the fiber end relative to another fiber optic component (e.g., a laser which outputs pulses of light, a sensor for receiving pulses of light, an end of a fiber belonging to another fiber optic cable, etc.) in order to minimize light energy loss.
Some fiber optic cables include multiple fibers (e.g., a bundle of fibers) which terminate at specialized connectors that position the ends of the fibers in a row (i.e., a row of fiber ends). A user can attach two of these cables together to form longer fiber optic pathways through the lengths of the two cables using a specialized coupling called an adaptor. The adaptor receives and holds the specialized connectors which terminate the ends of the cables.
One approach to aligning together two fiber optic connectors is called the pin-in-hole approach. Here, the user plugs the connector of a first cable into an adaptor, and then plugs the connector of a second cable into the adaptor such that the row of fiber ends of the first cable face a corresponding row of fiber ends of the second cable. A pair of metal pins residing on the ends of the row of fiber ends of the first cable extend outward in a direction parallel to the fibers. The metal pins are located and held in the ferrule. As the user plugs the cable of the second connector into the adaptor, this pair of metal pins inserts into corresponding holes residing on the ends of the row of fiber ends of the second cable to properly position the two connectors relative to each other. Once the fiber ends of the first cable are properly aligned with the fiber ends of the second cable, light from a fiber end of one cable can pass to a corresponding fiber end of the other cable with minimal light energy loss.
Fiber optic cables which have two, four, eight or 12 fibers typically terminate using connectors which configure the fiber ends into a single row configuration (e.g., a single row of two, four, eight or 12 fiber ends). A fiber optic cable having 24 fibers typically terminates in a double row configuration (e.g., two rows with each row having 12 fiber ends). In both the single row configuration and the double row configuration, a pair of metal pins, one at each end of the single or double row configuration, aligns the two connectors relative to each other.
Unfortunately, there are deficiencies to the above-described conventional pin-in-hole approach for connecting two fiber optic cables. For example, the conventional pin-in-hole approach relies on the placement of a pair of metal pins (one metal pin at each end of a single or double row configuration of fiber ends) to properly hold the fiber optic cable connectors in place relative to each other. As each metal pin inserts into its corresponding hole, any minor anomalies or subtle irregularities in the pins or connector bodies (e.g., a bent pin, an irregular pin hole, etc.) could result in a substantial stress on the connector bodies that either damages or distorts the connector bodies and prevents the fiber ends from aligning properly. In some cases, the stresses and distortions result in an air gap between the fiber ends which causes light energy loss between the fiber ends (e.g., due to lack of contact between corresponding fiber ends) and provides an area that can collect dirt. This is due, at least in part, to each metal pin having to restrain connector movement in multiple directions, e.g., along a direction perpendicular to the row of fiber ends (the X-direction), along a direction parallel to the row of fiber ends (the Y-direction), etc. This situation, which often involves the metal pins competing with each other, is typically referred to as an overconstrained situation.
Additionally, the metal pins typically concentrate connector stiffness and alignment near the center of the row configuration of fiber ends held within the connectors. As a result, the fiber ends at the center of the row configuration are typically aligned properly. However, the fiber ends toward the ends of the row configuration and near the metal pins, i.e., the metal pins furthest away from the center, can easily be misaligned and/or have air gaps therebetween. In some situations, such misalignment can cause a loss of light energy through the fiber optic pathways formed by the two connected cables (e.g., due to air gaps, collected dirt, lack of contact between fiber ends, etc.), or in extreme cases, complete loss of a light signal.
Furthermore, the sides of the ferrule having the exposed fiber ends are often polished to improve surface quality (e.g., to remove surface defects) to minimize light energy loss between fibers and such polishing, in some situations, tends to exacerbate the loss of light energy exchanged between some fiber ends. In particular, such polishing tends to leave the fiber ends near the center of the row at clean right angles (i.e., perpendicular) for optimal light exchange, but tends to taper the fiber ends toward the edges of the row such that the fiber ends near the ends of the row typically have non-perpendicular surfaces. If there is no compensation for the non-perpendicular surfaces of these fiber ends (e.g., pressure placed on the fiber ends to make them perpendicular, joining with other fiber ends having complementary non-perpendicular surfaces, etc.), air gaps (a source of high light energy loss) will form between the fiber ends resulting in lack of contact between corresponding fiber ends and less than optimal light transfer. As such, the amount of lost light energy tends to be greatest through the fiber ends near the ends of the fiber end row where tapering results in non-perpendicular fiber end surfaces.
In contrast to the above-described conventional pin-in-hole approach to connecting fiber optic cables, the invention is directed to techniques for forming a fiber optic connection through the application of kinematic coupling concepts to properly align corresponding fiber ends (e.g., a xe2x80x9cperfectly constrainedxe2x80x9d situation). A thorough discussion of kinematic coupling concepts is found in a book entitled, xe2x80x9cPrecision Machine Design,xe2x80x9d by Alexander H. Slocum, Prentice-Hall, Englewood Cliffs, N.J., 1992.
The fiber optic connection forms between a first connection assembly that provides alignment members and a second connection assembly that provides grooves such that a central axis of each groove of the second connection assembly is substantially perpendicular with a central axis of a corresponding alignment member of the first connection assembly. Each alignment member/groove pair can be positioned and oriented to control positioning of the first and second connection assemblies relative to each other in a single direction while allowing movement in other directions to prevent physical stressing of the connection assemblies. That is, the alignment members of the first connection assembly can be arranged around a periphery of a first array of fiber ends of a first fiber optic cable, and the grooves of the second connection assembly can be arranged around a periphery of a second array of fiber ends of a second fiber optic cable such that the aggregate contribution of each alignment member/groove pair forms a self-aligning mechanism that properly aligns the first and second arrays of fiber ends and minimize creation of air gaps between corresponding fiber ends (i.e., lack of contact between fiber ends) to provide effective light transfer between fiber optic cables.
The invention is based in part on the observation that physical bodies (e.g., fiber optic connectors) have six degrees of freedom (lateral movement in the X, Y and Z directions as well as rotation movement around the X, Y and Z axes). Since each groove controls movement of a corresponding alignment member in a direction that is perpendicular to a central axis of the groove, but allows movement in other directions (e.g., a direction along the central axis), less stress is placed on the connectors bodies (i.e., the connector housings forming the alignment member and the grooves) relative to the stress placed on conventional pin-in-hole connection systems which attempt to control movement of two fiber optic cable connectors using two metal pins inserted into two corresponding holes. Accordingly, the grooves and corresponding alignment members of the invention provide improved kinematic alignment with less distortion and strain that would otherwise result in improper alignment of fiber ends.
One arrangement of the invention is directed to a connection system having a first connection assembly, a second connection assembly and a coupling assembly. The first connection assembly has a first fiber optic cable portion and a first connector fastened to an end of the first fiber optic cable portion. The first connector has a housing and alignment members that extend from the housing. The second connection assembly has a second fiber optic cable portion and a second connector fastened to an end of the second fiber optic cable portion. The second connector has a housing that defines grooves. The coupling assembly couples the first connector of the first connection assembly with the second connector of the second connection assembly such that (i) the end of the first fiber optic cable portion faces the end of the second fiber optic cable portion and (ii) a central axis of each groove defined by the housing of the second connector is substantially perpendicular with a central axis of a corresponding alignment member of the first connector. Accordingly, each alignment member/groove pair can control movement in one direction (i.e., a direction perpendicular to the central axis of the groove) but allow movement in other directions (e.g., along the central axis of the groove, toward/away from the groove, etc.) thus preventing unnecessary stress on the connectors that would otherwise cause the fiber optic cable portion to align improperly.
In one arrangement, the central axes of the grooves intersect at an intersection point. For example, the end of the second fiber optic cable portion can include an Mxc3x97N array of fiber ends (M and N being positive integers greater than 1), and the intersection point can reside within the Mxc3x97N array of fiber ends. This arrangement enables the stiffness of the second connector to be focused within the Mxc3x97N array (e.g., a square array). Accordingly, when the alignment members of the first connector engage the grooves of the second connector, a corresponding Mxc3x97N array of fiber ends of the first fiber cable will tend to properly align with the Mxc3x97N array of the second connector.
In another arrangement, the housing of the second connector defines, for each groove, at least two planar surfaces such that the corresponding alignment member for that groove contacts the housing at two locations when the first connector of the first connection assembly couples with the second connector of the second connection assembly. Such contact at the two locations for each alignment member/groove pair enables repeatability, i.e., consistent placement of that alignment member within the corresponding groove each time the first and second connectors connect with each other so that the fiber ends of each cable align with each other in a consistent manner.
In one arrangement, the housing of the first connector includes a base portion and a floating portion that is movable relative to the base portion. In this arrangement, the floating portion defines the alignment members. In one arrangement, the first connection assembly further includes springs disposed between the base portion and the floating portion of the first connector, and the floating portion is rigidly attached to the end of the first fiber optic cable portion such that the end of the first fiber optic cable portion is movable relative to the base portion. In this arrangement, the springs provide a consistent and uniform force that pushes the floating portion of the first connector into position relative to the second connector. The grooves of the second connector guide the alignment members defined by the floating portion so that the end of the first fiber optic cable portion properly faces the end of the second fiber optic cable portion.
The features of the invention, as described above, may be employed in fiber optic connection systems, devices and methods as well as other fiber optic components such as those manufactured by Teradyne, Inc. of Boston, Mass.